I’m trying to build iwlwifi module manually and for my needs.
https://git.kernel.org/pub/scm/linux/kernel/git/iwlwifi/iwlwifi-fixes.git/tree/net/wireless/
When I run Makefile as make, I get:
subcmd-util.h: In function ‘xrealloc’:
subcmd-util.h:58:31: error: pointer ‘ptr’ may be used after ‘realloc’ [-Werror=use-after-free]
58 | ret = realloc(ptr, 1);
| ^~~~~~~~~~~~~~~
subcmd-util.h:52:21: note: call to ‘realloc’ here
52 | void *ret = realloc(ptr, size);
| ^~~~~~~~~~~~~~~~~~
subcmd-util.h:56:23: error: pointer ‘ptr’ may be used after ‘realloc’ [-Werror=use-after-free]
56 | ret = realloc(ptr, size);
| ^~~~~~~~~~~~~~~~~~
subcmd-util.h:52:21: note: call to ‘realloc’ here
52 | void *ret = realloc(ptr, size);
| ^~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[4]: *** [/data/iwlwifi-fixes/tools/build/Makefile.build:97: /data/iwlwifi-fixes/tools/objtool/help.o] Error 1
make[3]: *** [Makefile:59: /data/iwlwifi-fixes/tools/objtool/libsubcmd-in.o] Error 2
make[2]: *** [Makefile:63: /data/iwlwifi-fixes/tools/objtool/libsubcmd.a] Error 2
make[1]: *** [Makefile:69: objtool] Error 2
make: *** [Makefile:1349: tools/objtool] Error 2
Why is it? How to fix it?
No objections to your answer to the OP’s question, but as a curiosity, I’m trying to figure out what the original xrealloc() function is trying to do.
So far as I can tell, it tries a normal realloc() with the requested size, but if that fails, tries again with size=1. But strangely, it that fails, tries using the requested size a second time. And if that still fails, tries once more with size=1.
The POSIX man page isn’t giving me any hints as to why size=1 might be special, or if this is some sort of Linux-specific behavior or workaround. I wondered if you might have some insight why this function is the way it is.
Note: I’m on mobile, so haven’t checked the Git Blame history yet.
So
realloc(ptr, 1)only happens when!ret && !sizei.e. the call failed andsize == 0.Presumably this is to support a size of zero even when the underlying realloc does not.
The code is duplicated to try the realloc twice before failing.
I’m not sure what the use case of zero size is though.
Thanks for the explanation! I figured there was something odd, in combination with me reading the code too quickly.